Pythonidae Fitzinger, 1826, 1861

Szyndlar, Zbigniew & Georgalis, Georgios L., 2023, An illustrated atlas of the vertebral morphology of extant non-caenophidian snakes, with special emphasis on the cloacal and caudal portions of the column, Vertebrate Zoology 73, pp. 717-886 : 717

Pythonidae Fitzinger, 1826

General information.

Pythonids comprise some the largest and most impressive snakes of all time ( Murphy and Henderson 1997). Their fascinating nature is aptly imprinted also in their etymology, with the namesake type genus Python Daudin, 1803, named after the mythical serpent (Πύθων) that was guarding the Oracle of Delphi in Greek mythology. Pythons were long lumped for many decades into an expansive Boidae (see the respective entry above), although still certain early workers treated them as a distinct family (e.g., Cope 1864, 1887, 1893, 1898; Zittel 1887-1890; Lydekker 1888; Hoffmann 1890; Bocage 1895). Nevertheless, in all recent taxonomic schemes they are ubiquitously placed in their own distinct family ( Vidal and Hedges 2009; Schleip and O’Shea 2010; Pyron et al. 2013; Wallach et al. 2014; Barker et al. 2015; Zheng and Wiens 2016; Burbrink et al. 2020; Georgalis and Smith 2020; Boundy 2021; Ivanov 2022; Smith and Georgalis 2022).

Molecular data and fossil evidence support the origination of pythonids already by the Paleogene ( Esquerré et al. 2020; Zaher and Smith 2020). As a matter of fact, pythonids have a relatively rich fossil record, including also remains of the extant genera Python ( Hoffstetter 1964; Rage 1976, 2008b; Szyndlar 1991a; Ivanov 2000; Szyndlar and Rage 2003; Delfino et al. 2004, 2018; Head 2005; Ivanov and Böhme 2011; Georgalis et al. 2020a, 2020b; Head and Müller 2020; Ivanov et al. 2020; Singh et al. 2022a, 2022b), Morelia ( Scanlon 2001), and Liasis Gray, 1842 ( Scanlon and Mackness 2001).

Pythons comprise more than 40 extant species, distributed over large parts of Africa, Asia, and Australia ( Schleip and O’Shea 2010; Wallach et al. 2014; Boundy 2021). This moderate diversity of species is reflected in a wide spectrum of sizes (ranging from approximately 0.5 m to 9 m in length) and large disparity of body forms and life habits. There is still no consensus on the number of valid genera, with the past few decades witnessing splitting or lumping of available genera based on molecular and/or morphological evidence (e.g., Stimson 1969; McDowell 1975; Cogger et al. 1983; Wells and Wellington 1984, 1985; Underwood and Stimson 1990; Kluge 1993a; Harvey et al. 2000; Rawlings et al. 2008; Pyron et al. 2013; Reynolds et al. 2014; Schleip 2014; Barker et al. 2015; Esquerré et al. 2020, 2021; Kaiser et al. 2020). This is particularly true for the Australo-Papuan species, which have frequently and radically changed generic allocations within at least 11 genera ( Antaresia Wells and Wellington, 1984, Apodora Kluge, 1993, Bothrochilus Fitzinger, 1843, Chondropython Meyer, 1874, Leiopython Hubrecht, 1879, Liasis , Morelia , Nawaran Esquerré et al., 2020, Nyctophilopython Wells & Wellington, 1985, Python , and Simalia Gray, 1849) (see e.g., Stimson 1969; McDowell 1975; Cogger et al. 1983; Wells and Wellington 1984, 1985; Stimson and McDowell 1986; ICZN 1988; Underwood and Stimson 1990; Harvey et al. 2000; Rawlings at al. 2008; Pyron et al. 2013; Reynolds et al. 2014; Schleip 2014; Barker et al. 2015; Esquerré et al. 2020, 2021; Kaiser et al. 2020) - the only notable exception is the genus Aspidites Peters, 1877, whose validity and taxonomic content have remained stable.

In the present paper, we treat the vertebral description of the Australo-Papuan genera Antaresia , Bothrochilus , Leiopython , Liasis , and Simalia collectively, as the vertebral differences among these are not too important (see entry of Simalia below). This approach has been also applied in palaeontological literature, where only skeletal material was available and therefore an expansive concept of Liasis (sensu lato) was followed (e.g., Scanlon 2001; Scanlon and Mackness 2001). Moreover, these genera ( Antaresia , Apodora , Bothrochilus , Leiopython , Liasis , and Simalia ) form a monophyletic group when non-skeletal characters are excluded ( Kluge 1993a; see also Scanlon 2001; Scanlon and Mackness 2001). A similar rationale applies to the case of the Asian Python reticulatus , which is placed in its own genus Malayopython Reynolds, Niemiller & Revell, 2014 (see Reynolds et al. 2014), but we treat its description collectively with Python spp. On the other hand, we treat Morelia and Aspidites on their own, because of some peculiarities observed in their vertebrae.

Vertebrae of most pythonids closely resemble one another. At the same time they are very similar to those of most boids, displaying the same generalized morphological pattern: they are usually relatively short, wide, and massive, provided with vaulted neural arches, high neural spine and reduced prezygapophyseal accessory processes. A principal characteristic feature of most pythons (except for Python curtus and Python brongersmai ) is the very high amount of vertebrae, exceeding values observed in most other living snakes (with the exception of the leptotyphlopid Rhinoleptus and the typhlopid Letheobia ; see the respective entries above); the total number of vertebrae in pythonids is higher than 300, in some species more than 400 (see also "Parts of the vertebral column" above for the case of Nyctophilopython oenpelliensis which could potentially have an even higher vertebral count). It is further worth noting that complete fossil skeletons of snakes from Konservat-Lagerstätten localities demonstrate that high counts of vertebrae occurred in fossil Booidea (notably Eoconstrictor Scanferla & Smith, 2020, and Messelophis Baszio, 2004) but, strangely, not in fossil Pythonidae ( Baszio 2004; Scanferla and Smith 2020a; Zaher and Smith 2020). For detailed vertebral counts of extant pythonid taxa, see the respective entries of the genera below.

Similarly to boas, pythonid vertebrae were among the first to be presented in early snake anatomical works. This was apparently due to the fascination and general interest surrounding pythons as well as their large size, which therefore consequently rendered them easier to dissect. The first comprehensive documentation of pythonid vertebrae was conducted by D’Alton (1836), who provided extensive descriptions and figures of (both trunk and caudal) vertebrae of Python . Since then, numerous illustrations of vertebrae of different species of pythons were fairly often published by various authors. Principal examples of previous figures of vertebrae of extant Pythonidae were presented by Owen (1841, 1850, 1857, 1877), Rochebrune (1881), Albrecht (1883), Hoffmann (1890), Smith (1943), Romer (1956), Holman (1967), Hoffstetter and Gasc (1969), Gasc (1974), Underwood (1976), Holman (1982), Rage (1984), Palci et al. (2013a, 2013b, 2018, 2020), Xing et al. (2018), Garberoglio et al. (2019), Georgalis and Scheyer (2019), Fachini et al. (2020), Palci et al. (2020), and Shi et al. (2023b), including also from individuals of earlier ontogenetic stages ( Xing et al. 2018). Among these, vertebrae from the cloacal and/or caudal series have received considerably less attention, being figured solely by Rage (1984) and Palci et al. (2020). Figures of the microanatomy and histology / transverse sections of pythonid vertebrae were presented by Hoffstetter and Gasc (1969) and Houssaye et al. (2013). Quantitative studies on the intracolumnar variability of pythonid vertebrae were conducted by Gasc (1974) and Scanlon and Mackness (2001).